Thermal conditioning for integrated circuit testing

Abstract

Method and apparatus for thermally conditioning a microchip is described. The microchip ( 104 ) is thermally conditioned responsive to a temperature target over an interval of time. A diode voltage of a diode ( 503 ) of the microchip ( 104 ) is measured from which diode temperature is determined. The diode temperature is compared with the temperature target to determine a temperature error. This thermal conditioning may be repeated, where interval times are adjustable responsive to temperature error, until a stabilization band ( 401 ) is reached. Because a diode ( 503 ) of the microchip ( 104 ) is used, junction temperature, as opposed to external surface temperature of the microchip package, is obtained. Accordingly, a thermocouple attached to the external surface of the microchip is not needed.

1. A test system for testing a microchip, the microchip having a diode electrically accessible via an input pin and an output pin of the microchip, comprising:
 a tester;  
 a temperature forcing unit;  
 a programmed computer;  
 the programmed computer coupled to the tester and the temperature forcing unit;  
 the programmed computer programmed with a temperature control program, the temperature control program configured to:  
 obtain a temperature target;  
 cause the temperature forcing unit to thermally adjust temperature of the, microchip toward the temperature target;  
 wait for a first interval of time;  
 measure diode output voltage after the first interval of time; and  
 determine junction temperature proximal to the diode from the diode output voltage measured.  
 
   
   
     2. The test system, according to  claim 1 , wherein the tester is configured to provide a fixed current directed to the input pin for generation of the diode output voltage. 
   
   
     3. The test system, according to  claim 2 , wherein the temperature control program is configured to prompt the test system to provide the fixed current to the input pin. 
   
   
     4. The test system, according to  claim 1 , wherein the temperature control program is configured to determine a temperature error. 
   
   
     5. The test system, according to  claim 4 , wherein the temperature error is determined by subtracting the junction temperature determined from the temperature target. 
   
   
     6. The test system, according to  claim 5 , wherein the junction temperature is equal to:
   ( A=V (T))/ B,    
 
     where A and B are constants and V(T) is the diode output voltage measured. 
   
   
     7. The test system, according to  claim 4 , wherein the temperature control program is configured to provide a revised temperature target. 
   
   
     8. The test system, according to  claim 7 , wherein the revised temperature target is the temperature target plus the temperature error. 
   
   
     9. The test system, according to  claim 7 , wherein the temperature control program is configured to:
 (a) obtain the revised temperature target;  
 (b) cause the temperature forcing unit to thermally adjust temperature of the microchip toward the revised temperature target;  
 (c) wait for a second interval of time;  
 (d) measure diode output voltage after the second interval of time; and  
 (e) determine the junction temperature anew from the diode output voltage measured after the second interval of time.  
 
   
   
     10. The test system, according to  claim 9 , wherein the temperature control program is configured to determine the temperature error anew from the diode output voltage measured after the second interval of time and the revised temperature target, to provide the revised temperature target anew by adding the temperature error anew to the revised temperature target, and to repeat (a) through (e) until the temperature error anew is within a first threshold range. 
   
   
     11. The test system, according to  claim 10 , wherein the temperature control program is configured to wait for a third interval of time. 
   
   
     12. The test system, according to  claim 11 , wherein the temperature control program is configured to repeat (a) through (e) using a fourth interval of time in place of the second interval of time. 
   
   
     13. The test system, according to  claim 12 , wherein the temperature control program is configured to determine the temperature error anew from the diode output voltage measured after the fourth interval of time, and to repeat (a) though (e) using the fourth interval of time until the temperature error anew is within a second threshold range. 
   
   
     14. The test system, according to  claim 13 , wherein the second threshold range is smaller than the first threshold range. 
   
   
     15. A signal-bearing medium containing a program which, when executed by a processor in response to receiving thermal profile input, causes execution of a method comprising:
 obtaining an initial temperature target;  
 causing a temperature forcing unit to thermally adjust temperature of a microchip toward the initial temperature target, the microchip having a diode;  
 waiting for a first interval of time;  
 measuring diode output voltage of the diode after the first interval of time; and  
 determining junction temperature proximal to the diode from the diode output voltage measured.  
 
   
   
     16. The signal-bearing medium, according to  claim 15 , wherein the method further comprises:
 determining a temperature error; and  
 producing a revised temperature target by combining the temperature error and the initial temperature target.  
 
   
   
     17. The signal-bearing medium, according to  claim 16 , wherein the method further comprises:
 (a) obtaining the revised temperature target;  
 (b) causing the temperature forcing unit to thermally adjust temperature of the microchip toward the revised temperature target;  
 (c) waiting for a second interval of time;  
 (d) measuring diode output voltage after the second interval of time; and  
 (e) determining the junction temperature anew from the diode output voltage measured after the second interval of time.  
 
   
   
     18. The signal-bearing medium, according to  claim 17 , wherein the method further comprises:
 determining the temperature error anew from the diode output voltage measured after the second interval of time and the revised temperature target;  
 producing the revised temperature target anew by adding the temperature error anew to the revised temperature target; and  
 repeating the steps (a) through (e) until the temperature error anew is within a first threshold range.  
 
   
   
     19. The signal-bearing medium, according to  claim 18 , wherein the method further comprises waiting for a third interval of time. 
   
   
     20. The signal-bearing medium, according to  claim 19 , wherein the method further comprises repeating the steps (a) through (e) using a fourth interval of time in place of the second interval of time. 
   
   
     21. The signal-bearing medium, according to  claim 20 , wherein the method further comprises:
 determining the temperature error anew from the diode output voltage measured after the fourth interval of time; and  
 repeating the steps (a) though (e) using the fourth interval of time until the temperature error anew is within a second threshold range.  
 
   
   
     22. The signal-bearing medium, according to  claim 21 , wherein the first interval of time is an initial stabilization interval, wherein at least one of the second interval of time is a coarse adjustment interval, wherein the third interval of time is a coarse stabilization interval, and wherein at least one of the fourth interval of time is a fine adjustment interval. 
   
   
     23. The signal-bearing medium, according to  claim 21 , wherein the first threshold range is a coarse adjustment threshold range, and wherein the second threshold range is a stability band. 
   
   
     24. A method for thermally conditioning a microchip, the method comprising:
 setting an initial temperature target;  
 thermally conditioning the microchip responsive to the initial temperature target over an initial stabilization interval;  
 measuring a first diode voltage of a diode of the microchip;  
 determining a first diode temperature responsive to the first diode voltage measured;  
 comparing the first diode temperature with the initial temperature target to determine a first temperature error;  
 (a) generating a coarse temperature target responsive to the first temperature error and the initial temperature target;  
 (b) thermally conditioning the microchip responsive to the coarse temperature target over a coarse adjustment interval;  
 (c) measuring a second diode voltage of the diode of the microchip after the coarse adjustment interval;  
 (d) determining a second diode temperature responsive to the second diode voltage measured;  
 (e) comparing the second diode temperature with the coarse temperature target to determine a second temperature error;  
 thermally conditioning the microchip over a coarse stabilization interval;  
 (f) generating a fine temperature target responsive to the second temperature error and the coarse temperature target;  
 (g) thermally conditioning the microchip responsive to the fine temperature target over a fine adjustment interval;  
 (h) measuring a third diode voltage of the diode of the microchip after the fine adjustment interval;  
 (i) determining a third diode temperature responsive to the third diode voltage measured; and  
 (j) comparing the third diode temperature with the fine temperature target to determine a third temperature error.  
 
   
   
     25. The method, according to  claim 24 , wherein the coarse temperature target, the second diode voltage, the second diode temperature and the second temperature error are generated from one or more iterations of the steps (a) through (e). 
   
   
     26. The method, according to  claim 25 , wherein the fine temperature target, the third diode voltage, the third diode temperature and the third temperature error are generated from one or more iterations of the steps (f) through (j).